I don't really do backlogs too much, the idea of it never stuck with me. I always play what I buy. That said, I feel like that's changed a bit this year with some games I've yet to play. Those being, let's see here...
Pathologic 2 - I got this because a friend loved the first game and wanted to play this. In truth, I thought he had already played this one and loved it too, but he hadn't. Anyways, I don't think it's my kind of thing. Interesting, but I doubt I'll ever go back and finish it.
The Witcher - same friend wanted me to play through the Witcher trilogy. I asked if I could play the third game only, but 1 and 2 were super cheap and he told me to play the whole thing. I can't say this game is good lol. I feel like skipping to 3 already, but maybe I'll play this someday.
Mass Effect 2 - same friend wanted me to play through the Mass Effect trilogy. I replayed the first game and loved it all over again, and then stopped partway through the second game because I didn't enjoy it all over again. Definitely wanna insist on this one, though.
Deus Ex - I've been somewhat intrigued by this series ever since I started hosting the greatest games event and seeing many people list them, and after playing the Guardians game and seeing how awesome the whole team at Eidos-Montréal seems to be, intrigue became interest. Then black friday came and the whole series went on a ridiculously cheap sale at GOG, so I got them all, but I haven't started them yet.
So that's 4 games, but I suppose it's 10 if you include all the other ones from trilogies/series I haven't started yet.